1. Field of the Invention
The present invention relates to an arteriosclerosis diagnosing apparatus for diagnosing arteriosclerosis or arteriosclerotic lesion, in particular, atherosclerosis.
2. Related Art Statement
There are known three sorts of arteriosclerosis; atherosclerosis is atheromatous sclerosis of endothelium of large or medium arteries, mediosclerosis is calcification of media of arteries, and arteriolosclerosis is sclerosis of small arteries.
Meanwhile, pulse-wave-propagation-velocity-related information that is related to a velocity at which a pulse wave propagates between two regions of a living subject, e.g., pulse-wave propagation velocity itself or pulse-wave propagation time, may be measured to diagnose whether the subject has atherosclerosis or not, or what degree of atherosclerosis the subject has. If a pulse-wave propagation velocity as a sort of pulse-wave-propagation-velocity-related information is measured from an atherosclerotic region of the subject, the measured velocity is higher than a normal velocity, if a degree of the atherosclerosis is low; and the measured velocity is lower than the normal velocity, if the degree of atherosclerosis is medium or high. Thus, the pulse-wave-propagation-velocity-related information can be used to diagnose whether the subject has atherosclerosis, or what degree of atherosclerosis the subject has.
The reason why a measured pulse-wave propagation velocity is higher than a normal velocity if a degree of atherosclerosis is low and the measured velocity is lower than the normal velocity if the degree of atherosclerosis is medium or high, is as follows: As atherosclerosis that is also called arteriostenosis advances, the inner diameters of arteries decrease. Since blood pressure lowers downstream of the arteriostenotic region, pulse-wave propagation velocity that changes with the blood pressure also lowers. Meanwhile, since mediosclerosis is calcification of media, the pulse-wave propagation velocity increases as the mediosclerosis advances. Generally, the mediosclerosis advances with the atherosclerosis. In the case where the degree of atherosclerosis is low, the influence of mediosclerosis is stronger than that of the atherosclerosis and accordingly the pulse-wave propagation velocity is higher than the normal velocity. However, in the case where the degree of atherosclerosis is medium or high, the influence of atherosclerosis is stronger than that of the mediosclerosis and accordingly the pulse-wave propagation velocity is lower than the normal velocity.
Pulse-wave propagation velocity has the above-described relationship with atherosclerosis and mediosclerosis. Since, however, the present invention relates to an apparatus for diagnosing atherosclerosis or arteriostenosis, the following description employs such a definition that arteriosclerosis means atherosclerosis, unless it otherwise specifies.
There is known an inferior-and-superior-limb blood-pressure-index measuring apparatus as a sort of arteriosclerosis diagnosing apparatus. This apparatus is disclosed in, e.g., Japanese Patent No. 3,140,007 or its corresponding U.S. Pat. No. 6,355,000. The inferior-and-superior-limb blood-pressure-index measuring apparatus includes two cuffs that are adapted to be worn on an inferior limb and a superior limb of a living subject, calculates, as an inferior-and-superior-limb blood-pressure-index, a ratio of one of a superior-limb blood pressure and an inferior-limb blood pressure to the other, and diagnoses arteriosclerosis based on the thus calculated inferior-and-superior-limb blood-pressure-index. If this apparatus is so modified as to be able to obtain pulse-wave-propagation-velocity-related information so as to assure the reliability of inferior-and-superior-limb blood-pressure-index, then the apparatus would be able to more accurately diagnose arteriosclerosis. If the two cuffs employed to measure the superior-limb blood pressure and the inferior-limb blood pressure are used to detect respective pulse waves from the superior limb and the inferior limb, the thus detected two pulse waves would be able to be used to determine a pulse-wave propagation time. Thus, the pulse-wave propagation time as another sort of pulse-wave-propagation-velocity-related information would be able to be obtained without needing to employing any additional sensors.
In many cases, arteriosclerosis occurs to inferior limbs only. However, in some cases, arteriosclerosis occurs to superior limbs as well. A pulse-wave propagation time measured from a superior limb and an inferior limb means a difference between a time of propagation of a pulse wave from the heart to the superior limb and a time of propagation of the pulse wave from the heart to the inferior limb. Therefore, in those cases, even if the inferior limb has arteriosclerosis and accordingly a time of propagation of pulse wave from the heart to the inferior limb increases, a pulse-wave propagation time measured from the superior limb and the inferior limb, or a pulse-wave propagation velocity determined based on the measured propagation time falls in a normal range, if the superior limb has arteriosclerosis and accordingly a time of propagation of pulse wave from the heart to the superior limb increases. Thus, in the above-indicated cases, the pulse-wave-propagation-velocity-related information obtained from the superior and inferior limbs cannot be used to diagnose arteriosclerosis with high accuracy.
Meanwhile, there are some cases where noise produced by a physical motion of a living subject is mixed with pulse waves and accordingly respective reference points of those pulse waves that are to be used to obtain pulse-wave propagation-velocity-related information cannot be accurately detected. In those cases, the pulse-wave-propagation-velocity-related information cannot be obtained with accuracy. In addition, if arrhythmia occurs to a living subject, respective reference points of two pulse waves to be used to obtain pulse-wave propagation-velocity-related information may not be accurately detected, and accordingly the pulse-wave-propagation-velocity-related information may not be obtained with accuracy. If pulse-wave-propagation-velocity-related information cannot be obtained with accuracy, then arteriosclerotic legion cannot be diagnosed with accuracy.
It is therefore an object of the present invention to provide an arteriosclerosis diagnosing apparatus for diagnosing arteriosclerosis or arteriosclerotic lesion with high accuracy.
The above object has been achieved by the present invention. According to a first aspect of the present invention, there is provided an apparatus for diagnosing arteriosclerosis of a living subject, comprising an inflatable cuff which is adapted to be wound around a first portion of the subject to press said first portion with a pressing pressure; a pulse-wave detecting device which detects a pulse wave that is produced from an artery of said first portion of the subject pressed by the cuff with the pressing pressure and is transmitted to the cuff; and an arteriosclerosis judging means for judging, based on a change of the pulse wave caused by a change of the pressing pressure of the cuff, whether there is an arteriosclerotic lesion in a second portion of the subject that is located upstream of said first portion in a direction in which blood flows in the artery.
If the subject has arteriosclerosis in the second portion located upstream of the first portion around which the cuff is wound, the sharpness of shape of the pulse wave detected from the first portion by the pulse-wave detecting device significantly decreases at a lower pressing pressure of the cuff than a pressing pressure at which the sharpness of shape of a pulse wave detected from a first portion located downstream of a second portion free of arteriosclerosis significantly decreases. Therefore, the arteriosclerosis judging means can judge, based on the change of the pulse wave caused by the change of the pressing pressure of the cuff, whether there is arteriosclerosis in the second portion located upstream of the first portion around which the cuff is wound.
If the above-described principle is applied to the left and right superior limbs, arteriosclerosis of an inferior limb can be accurately diagnosed based on pulse-wave-propagation-velocity-related information obtained from the inferior limb and one of the two superior limbs. According to a second aspect of the present invention, there is provided an apparatus for diagnosing arteriosclerosis of an inferior limb of a living subject, comprising a left-superior-limb cuff which is adapted to be wound around a left superior limb of the subject to press the left superior limb with a first pressing pressure; a right-superior-limb cuff which is adapted to be wound around a right superior limb of the subject to press the right superior limb with a second pressing pressure; an inferior-limb cuff which is adapted to be wound around the inferior limb of the subject; a left-superior-limb pulse-wave detecting device which detects, as a left-superior-limb pulse wave, a pulse wave which is produced from an artery of the left superior limb pressed by the left-superior-limb cuff with the first pressing pressure and is transmitted to the left-superior-limb cuff; a right-superior-limb pulse-wave detecting device which detects, as a right-superior-limb pulse wave, the pulse wave which is produced from an artery of the right superior limb pressed by the right-superior-limb cuff with the second pressing pressure and is transmitted to the right-superior-limb cuff; an inferior-limb pulse-wave detecting device which detects, as an inferior-limb pulse wave, the pulse wave which is produced from an artery of the inferior limb pressed by the inferior-limb cuff and is transmitted to the inferior-limb cuff; a change-value calculating means for calculating a first change value representing a change of the left-superior-limb pulse wave caused by a change of the first pressing pressure of the left-superior-limb cuff, and a second change value representing a change of the right-superior-limb pulse wave caused by a change of the second pressing pressure of the right-superior-limb cuff; an arteriosclerosis judging means for judging, based on a comparison of the first and second change values calculated by the change-value calculating means, which is lower, a degree of arteriosclerosis of a first portion of the subject located between the heart of the subject and the left superior limb or a degree of arteriosclerosis of a second portion of the subject located between the heart and the right superior limb; and a pulse-wave-propagation-velocity-related-information obtaining means for obtaining, based on (a) one of the left-superior-limb pulse wave and the right-superior-limb pulse wave that corresponds to one of the first and second portions that has the degree of arteriosclerosis judged as being lower than the degree of arteriosclerosis of the other of the first and second portions by the arteriosclerosis judging means, and (b) the inferior-limb pulse wave detected by the inferior-limb pulse-wave detecting device, pulse-wave-propagation-velocity-related information that is related to a velocity at which the pulse wave propagates in the subject.
According to this aspect, the change-value calculating means calculates the first and second change values. The first change value represents the change of the left-superior-limb pulse wave caused by the change of the first pressing pressure of the left-superior-limb cuff, and the second change value represents the change of the right-superior-limb pulse wave caused by the change of the second pressing pressure of the right-superior-limb cuff. Thus, the first change value reflects a degree of arteriosclerosis of the first portion of the subject located between the heart and the left superior limb, and the second change value reflects a degree of arteriosclerosis of the second portion of the subject located between the heart and the right superior limb. Therefore, the arteriosclerosis judging means can judge, by comparing the first and second change values with each other, which is lower, the degree of arteriosclerosis of the first portion located between the heart and the left superior limb or the degree of arteriosclerosis of the second portion located between the heart and the right superior limb. The pulse-wave-propagation-velocity-related-information obtaining means obtains, based on the superior-limb pulse wave corresponding to one of the first and second portions that has the degree of arteriosclerosis judged as being lower by the arteriosclerosis judging means, and the inferior-limb pulse wave, the pulse-wave-propagation-velocity-related information. Thus, the present apparatus can obtain the pulse-wave-propagation-velocity-related information that is less influenced by the arteriosclerosis of the superior limbs. Therefore, the pulse-wave-propagation-velocity-related information can be used to diagnose accurately arteriosclerosis of the inferior limb.
According to a third aspect of the present invention, there is provided an apparatus for diagnosing arteriosclerosis of a living subject, comprising a first-pulse-wave detecting device including a first detecting portion which is adapted to be worn on a first body portion of the subject to detect, as a first pulse wave, a pulse wave produced from the first body portion; a second-pulse-wave detecting device including a second detecting portion which is adapted to be worn on a second body portion of the subject to detect, as a second pulse wave, the pulse wave produced from the second body portion; a synchronism judging means for judging whether the first pulse wave detected by the first-pulse-wave detecting device and the second pulse wave detected by the second-pulse-wave detecting device are synchronous with each other; and a pulse-wave-propagation-velocity-related-information obtaining means for obtaining, based on the first and second pulse waves judged as being synchronous with each other by the synchronism judging means, pulse-wave-propagation-velocity-related information that is related to a velocity at which the pulse wave propagates in the subject.
When noise is produced by a physical motion of the living subject, it may be mixed, at different timings, with two pulse waves detected from different regions of the subject. In this case, respective detected pulses of the two pulse waves may not be synchronous with each other. However, if the synchronism judging means judges that first pulse wave detected by the first pulse-wave detecting device and the second pulse wave detected by the second pulse-wave detecting device are synchronous with each other, then it can be said that the first and second pulse waves are free of the noise produced by the physical motion of the subject. The pulse-wave-propagation-velocity-related-information obtaining means obtains the pulse-wave-propagation-velocity-related information based on the first and second pulse waves judged as being synchronous with each other by the synchronism judging means. Thus, the present apparatus can obtain accurate pulse-wave-propagation-velocity-related information. Therefore, arteriosclerosis can be accurately diagnosed based on the thus obtained, accurate pulse-wave-propagation-velocity-related information.
According to a fourth aspect of the present invention, there is provided an apparatus for diagnosing arteriosclerosis of a living subject, comprising a first-pulse-wave detecting device including a first detecting portion which is adapted to be worn on a first body portion of the subject to detect, as a first pulse wave, a pulse wave produced from the first body portion; a second-pulse-wave detecting device including a second detecting portion which is adapted to be worn on a second body portion of the subject to detect, as a second pulse wave, the pulse wave produced from the second body portion; a normal-pulse-period-range determining means for determining a normal pulse-period range based on one of the first pulse wave detected by the first-pulse-wave detecting device and the second pulse wave detected by the second-pulse-wave detecting device; an arrhythmia judging means for judging, when one of a pulse period of the first pulse wave and a pulse period of the second pulse wave falls in the normal pulse-period range determined by the normal-pulse-period-range determining means, that the first and second pulse waves are not arrhythmic; and a pulse-wave-propagation-velocity-related-information obtaining means for obtaining, based on the first and second pulse waves judged as being not arrhythmic by the arrhythmia judging means, pulse-wave-propagation-velocity-related information that is related to a velocity at which the pulse wave propagates in the subject.
According to this aspect, the pulse-wave-propagation-velocity-related-information obtaining means obtains the pulse-wave-propagation-velocity-related information based on the first and second pulse waves judged as being not arrhythmic by the arrhythmia judging means. Thus, the present apparatus can obtain accurate pulse-wave-propagation-velocity-related information. Therefore, arteriosclerosis can be accurately diagnosed based on the thus obtained, accurate pulse-wave-propagation-velocity-related information.